Question

The cost of per litre of milk is Rs 15. Draw the graph for the relation between the quantity and cost. Hence, find

1. The proportionality constant

2. The cost of 3 litres of milk.

Answer 1

Let us form the following table

$\begin{array}{cccccc}Quantityofmilkinlitres\left(x\right)& 1& 2& 3& 4& 5\\ Costperlitre\left(y\right)& 15& 30& 45& 60& 75\end{array}$

From the table, we observe that as x increases, y also increases. Therefore, it is in direct variation.

We get y $\alpha$x (i.e.) y = kx

Since, $\frac{y}{x}$ =k, from the table, we find $\frac{15}{1}$ =$\frac{30}{2}$ = $\frac{45}{3}$ = $\frac{60}{4}$= $\frac{75}{5}$ = 15

Therefore, k = 15

Plot the points (1, 15), (2, 30), (3, 45), (4,60), (5,75).

From the graph, it is clear that the cost of 3 litres of milk is Rs. 45.